Casing centralizer



NOV. 1966 J. H. cosss ETAL 3,282,349

GAS ING CENTRALI ZER Filed Jan. 22, 1964 INVENTORS JAMES H. COBBS HERBERT L. BOLE V ASCENCION GONZALEZ ATTORNEYS United States Patent 3,282,349 CASING CENTRALIZER James H. Cobbs, Herbert L. Bolen, and Ascencion Gonzalez, all of Tulsa, Okla, assignors to Fenix & Scisson, Iuc., Tulsa, Okla, a corporation of Oklahoma Filed Jan. 22, 1964, Ser. No. 339,515 4 Claims. (Cl. 16624l) This invention relates to a centralizer for tubular stock. More particularly, this invention relates to a centralizer for centering a casing string in a bore hole to insure a uniform annulus space into which cement can be injected. This invention has specific application to centering large diameter casing strings in bore holes.

In drilling bore holes, such as oil or water wells and the like, it is customary to set at least one relatively large diameter casing string in the hole. The use of relatively large diameter bore holes as access shafts to subterranean mines has also found acceptance in the mining industry. It is generally preferred, if not required, that these access holes or shafts be provided with a large diameter casing for various reasons known to the art, such as to prevent cave-ins and allow more rapid movement of equipment, material and personnel therethrough.

A large diameter casing string is first positioned centrally within the bore hole, and then cement is injected into the annulus space, between the outside surface of the casing string and the interiorly exposed face of the bore hole. When the cement sets within this annulus space, it becomes bonded both to the bore hole face and to the surface of the casing string thereby producing a protective sheath for the string and also preventing movement of the string.

It is preferred, in order that the cementing of the casing string be most effective, that the thickness of the cement sheath surrounding the casing string be substantially equal on all sides of the casing. In order to accomplish this, it is necessary to center the casing throughout the length of the hole. This centering is accom plished by the use of various commercially available casing centralizers, which are attached to the outside surface of the casing and extend radially outwardly into contact with the internally exposed face of the borehole.

These centralizers assume many forms, some being solid or perforated annular rings, others consisting of outwardly extending resilient fingers, while still others are radially outwardly extending arms or springs. The common disadvantage of most of these commercially available centralizers is that they fail to provide the desired centering affect when used in a hole of varying diameter, while at the same time insuring a uniform minimum annulus space to accommodate the cement sheathe. Furthermore, because of their unyielding and rather bulky construction, many of these prior art centralizers often times hang up on irregularities in the face of the borehole, thereby greatly complicating the positioning of the casing string in the bore hole.

Therefore, it is an object of this invention to provide a casing centralizer that overcomes the disadvantages of the prior known oentralizers.

Another object of this invention is to provide a casing centralizer that is easily and economically manufactured, and is easy to apply exteriorly of the casing string.

Still another object of this invention is to provide a casing centralizer capable ofadjusting radially while running the casing string into the hole to allow passage of the casing string through a hole of varying diameter.

Yet another object of this invention is to provide a casing centralizer that insures a substantially uniform annular space surrounding the casing string for accommodating a cement sheathe to be set therein.

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Another object of this invention is to provide a centralizer having a relatively streamlined configuration which is not prone to becoming hung up in the bore hole.

A still further object of this invention is to provide a casing centralizer that is expansible between predetermined maximum and minimum limits with the minimum limit being preselected to insure a uniform annular space between the casing and the bore hole.

, Still another object of this invention is to provide a casing centralizer of the type described in which the minimum limit is easily and quickly variable in the field to accommodate changes in conditions, such as hole size, or casing size.

Still a further object of this invention is to provide a casing centralizer that is spaced in plurality both annularly around the casing string and longitudinally over the length of the casing string, that is variable in radial expansion between predetermined maximum and minimum limits with the minimum limit being easily adjusted in the field to insure a substantially uniform minimum annular space between the casing and the bore hole into which a cement sheathe can be formed.

Further objects and advantages of this invention will be apparent from the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

FIGURE 1 is a side elevational view of a portion of a casing string equipped with a plurality of the casing centralizers of this invention.

FIGURE 2 is a cross-sectional view taken along line 2-2 of FIGURE 1.

FIGURE 3 is an external view of the casing centralizer of this invention.

FIGURE 4 is a longitudinal cross-sectional view of the casing centralizer of this invention.

FIGURE 5 is an external view of the casing centralizer of this invention.

FIGURE 6 is a cross-sectional view taken along line 66 of FIGURE 4.

General description In general, the centralizer of this invention consists of a bridge support having an elongated top plate and two sides, each side depending from a longitudinal edge of the top plate; and a longitudinally arcuate leaf spring provided on its first end with a first substantially closed circular loop and provided on its second end with a second substantially closed circular loop. The first loop of the spring is pivotally retained within the space between a first end of the sides of the support with the first end portion of the spring extending through a first opening provided therefore in a top plate of the support, adjacent the first loop. The second loop is pivotally and longitudinally slidably retained in the space between the second end of the sides of the support with the second end portion of the spring extending through a second opening provided therefore in the top plate of the support, adjacent the second loop. The second loop is retained between the two sides of the support by a retainer element that 7 extends through registering longitudinal slots in the sides of the support and the central passage of the second circular loop.

The centralizer is attached to the exterior of a casing string, longitudinally parallel to the axis of the casing, along the bottom edges of the sides such that the top plate is spaced radially outwardly from the exterior surface of the casing and the bight portion of the spring extends radially outwardly from the top plate of the support.

:1; 9 Specific description For a more specific description of this invention, reference is now made to the drawings in general, and more specifically to FIGURES 3, 4 and 5, wherein is shown the casing centralizer 10, of this invention. Centralizer is made up of two basic elements; a bridge support 12 and an arcuate leaf spring 14.

Bridge support 12 is substantially trough shaped having a top 16 and two preferably parallel sides 18 and 20. Sides 18 and 211 are preferably flat and connect at right angles to the longitudinal edges of top 16. However, sides 18 and 26 can be of a different shape and can attach to top 16 at an angle other than 90 without departing from the scope of this invention. Top 16 is provided near one end thereof with a relatively small, preferably square or rectangular first opening 22 therein. A second opening 24 is provided in top plate 16 near the other end thereof, and is substantially larger than the first opening 22. Second opening 24 is also preferably square or rectangular shaped. Registering perforations 25 are pro vided, one each, in side plates 18 and 20, below first opening 22. Registering longitudinally elongated slots 26 are provided one each in sides 18 and 20, proximate to and below second opening 24.

Leaf spring 14 is substantially bow or arcuate shaped in transverse cross section and is provided on each end thereof with a single circular closed loop 28 and 36. As best seen in FIGURE 4, the looped ends 28 and 30 of spring 14 are retained in the space between the sides 18 and 26), adjacent to openings 22 and 24, respectively, with the end portions extending through openings 22 and 24 such that the bight portion 31 of the spring is spaced above the top 16 of bridge support 12.

Looped end 28 is retained within the space between the sides 18 and 20, adjacent opening 22, by a retainer element 32, such as a pin or bolt, that extends transversely of the centralizer 10, through registering perforations 25 and the loop 3%. Locking means, such as washer 33 and nut 34, are attached to each end of retainer pin 32, exteriorly of sides 18 and 26, to prevent withdrawal of pin 32. It is preferred that the inside diameter of loop 28 be slightly larger than the diameter of pin 32 to facilitate assembly of the centralizer 16 and to allow looped end 28 to rotate with relation to pin 32 and support bridge 12 as the spring 14 flexes during operation of the centralizer.

Looped end 31 is slidably and preferably rotatably retained within the space between the sides 18 and 20, adjacent opening 24, by a second retainer element 35, similar in construction to retainer element 32. Retainer element 35 is extended through registering slots 26 and the center of loop 31]. Looking means, such as washers 36 and nuts 38, are attached to the respective ends of the retainer element 35, exteriorly of and adjacent to the sides 18 and 20, to prevent its withdrawal from slots 26 and loop 36.

Retainer element 35 is preferably sufficiently small in diameter in relation to the width of slots 26 to allow longitudinal movement of the element within these slots. Therefore, looped end 36 of spring 14 is free to slide longitudinally throughout the limits of slots 26 as spring 14 flexes, that is, expands and retracts, during operation of the centralizer 10.

In this regard, it should be noted that opening 24 is preferably longitudinally longer than slots 26 and extends farther toward opening 22 than do slots 26. Therefore, the end porton of spring 14, adjacent looped end 36, that is inclined relative to top 16, will be accommodated in opening 24 even when the spring is expanded outwardly to its maximum extent with loop 30 located at the end f slots 26 closest looped end 28.

Furthermore, it should be understood that leaf spring 14 is pre-stressed such that the straight line distance between looped ends 28 and 30 is normally less than the distance between perforations 25 and the end of slots 4 26 nearest perforations 25. Therefore, under unrestricted conditions, looped end 30 tends to move toward the end of slots 26, nearest perforations 29, thereby expanding the bight portion 31 of the spring outwardly to its maximum distance.

In operation, it is preferred that the centralizers be arranged in a plurality of annular banks or groups, spaced longitudinally over that portion of the casing 4t) to be centered in a well bore (not shown). As is best seen in FIGURES 1 and 2 each annular group of centralizers consists of a plurality of preferably equally annularly spaced centralizers 10, each extending longitudinally parallel to the axis of casing 46 and attached to the exterior of the casing, as by a longitudinal weld 42 in the angle of juncture of the sides 18 and 26 and the casing 46.

The number of annular groups of centralizers 10 and their longitudinal spacing on casing 46 will be largely a matter of choice of the manufacturer and/or user. The number of centralizers 10 employed in each annular group will be largely determined by the diameter of casing 40. For smaller casing strings, as few as two or three centralizers 10 will be utilized in each annular group, whereas, for casing strings of the order of 42 inches in diameter 8 centralizers would be preferred.

When centralizers 1d are attached exteriorly of the casing 40 in the above described manner the bight portion 31 of spring 14 extends radially outwardly into rubbing contact with the exposed face of the bore hole (not shown) as the casing is positioned in the borehole. Therefore, the biasing force of springs 14 is applied equally around the periphery of the casing string 46 to center the casing string within the borehole 40.

When restrictions are encountered in the bore hole as the casing string 46 is moved longitudinally therein, springs 14 collapse inwardly relative to the bridge support 12 and casing string 40 thereby allowing the string to proceed past the restriction. As the spring collapses inwardly, that is tends to straighten out, looped end 30 slides longitudinally within slots 26 of sides 18 and 211 in a direction away from the first looped end 28. When relatively large diameter zones are encountered in the bore hole, springs 14 tend to expand outwardly maintaining rubbing contact with the exposed facial surface of the bore hole. Outward expansion of springs 14 is accompanied by a longitudinal movement of looped end 31) within slots 26 toward the first looped end 28 of spring element 14.

Therefore, it should be clear that spring 14 is free to expand and retract between minimum and maximum limits, which limits are set by the length of slots 26. When looped end 311 reaches the end of slots 26 nearest first looped end 28, the spring 14 is in its maximum expanded position. Likewise, when looped end 30 reaches the end of slots 26 spaced farthest from firs-t looped end 28, the spring 14 is in its minimum expanded position (maximum retracted position). Therefore, a minimum limit is imposed upon the radial offset of the casing string from the bore hole face, this limit corresponding approximately to the distance between the exterior surface of casing string 46 and the outermost point of bight portion 31 of spring 14 when spring 14 is expanded to its minimum limit as above described. This minimum radial offset assures an annular space between the casing and the bore hole of a predetermined minimum radial thickness to insure the formation of a substantially uniform annulus of suflicient radial thickness to provide the necessary casing protection and holding strength.

Referring now to FIGURE 5, there is shown a means for varying in the field, the minimum limit to which spring 14 can be expanded with respect to bridge support 12. This limit is easily varied by welding or otherwise attaching a relatively short metallic stop element 44 transversely across slots 26 at a point spaced from the end furtherest displaced from looped end 28 of spring element 14. By so positioning element 44 the effective length of slots 26 is reduced on the end farthest from first looped end 28 of spring 14 thereby reducing the amount to which spring element 14 can be flattened or straightened out.

Alternatively, centralizer of this invention can be manufactured having a plurality of these elements 44 arranged transversely along the length of slots 26 to be later removed as necessary to meet field requirements. Also, it should be noted that although elements 44 have been described as means for reducing the amount to which spring element 14 can be collapsed, it is contemplated that element 44 can be attached across slots 26 near the end closest to perforations 25 thereby decreasing the maximum amount to which spring 14 can be expanded or flexed outwardly.

As is evident from the figures, centralizer 10 presents an overall streamlined configuration therefore, is not likely to hang up on irregularities on the face of the bore hole to stick the casing as the casing is being moved axially in the hole. The centralizer 10 is mounted on the casing with only the bight portion of the spring 14 presented outwardly. Also, the sides 16 and 18 of support bridge 12 are tapered on the upper and lower ends upwardly and downwardly, respectively, toward the axis of the casing. Therefore, there are no sharp externally exposed angles, fingers or similar protuberances on centralizer 10 that could easily hang up in the bore hole.

It should be noted that by making bridge support 16 substantially trough shaped and open at both ends, as described, the annulus space between the exterior of casing 40 and the face of the bore hole remains relatively unobstructed to the flow of cement therethrough during cementing of the casing in the bore hole. Furthermore, there is little or no obstruction to the movement of well fluids and/ or bore hole drilling fluids relative to the casing as the casing is moved axially in the hole to position the casing preparatory to cementing it in place. During the cementing of casing 10 in the bore hole, the cement will freely enter into the space between sides 16 and 18 of each centralizers, thereby providing a uniform solid and strong protective sheath surrounding the casing.

It should be clear from the foregoing that this invention provides a casing centralizer that is especially applicable to centering relatively large diameter casing within a bore hole preparatory to injecting cement within the annulus space between the casing and the bore hole. However, although this centralizer has been described as being particularly applicable to centering large diameter casing in a bore hole, it is contemplated that it can be used to center any substantially tubular element, regardless of diameter, within an elongated substantially circular opening without departing from the scope of this invention.

Furthermore, this centralizer provided limited restriction on the size of the annulus space to prevent any obstruction of this annulus space to the flow of cement therethrough. Also, the centralizer of this invention is provided with means for limiting the amount of collapse of the centralizer thereby insuring at least minimum annulus volume.

The invention has been described by reference to specific and preferred embodiments. It will be apparent, however, that many modifications can be made without the departing from the spirit and scope of the invention. Accordingly, this invention should be construed not to be limited to the embodiment herein described, but should be limited only by the scope of the appended claims.

What is claimed:

1. A centralizer for attachment exteriorly to an externally substantially cylindrical body to center said body within a correspondingly circularly passage and assure at least a minimum spacing between the exterior of said body and the interior of said passage, said centralizer comprisan elongated support having at least one top plate and at least two spaced apart side plates depending one each from the longitudinal edges of said top plate, each of said side plates having free bottom edges for longitudinal attachment to said body;

a first opening provided through a first end portion of said top plate;

a second opening provided through a second end portion of said top plate, spaced longitudinally from said first opening;

two registering perforations provided one each in corresponding first end portions of said two side plates, proximate to and below said first opening;

two registering longitudinally elongated slots provided one each in corresponding second end portions of said side plates, proximate to and below said second opening;

an elongated longitudinally curved leaf spring provided on its first end with a longitudinally rolled substantially closed circular first loop and provided on its second end with a longitudinally rolled substantially closed circular second loop, said first loop located between said two side plates coaxial with said two perforations, with the first end portion of said spring extending through said first opening said second loop located between said two side plates with the central passage through said second loop registering with said two slots and with the second end portion of said spring extending through said second opening whereby the middle portion of said spring is spaced transversely outwardly from said top plate, said spring being prestressed such that said first loop and said second loop are normally urged toward each other into positions of straight line separation that is shorter than the shortest distance between said slots and said perforations;

a first retainer means extending through said two perforations and said first loop for pivotally attaching said first loop between said side plates;

a second retainer means extending through said two slots and said second loop for pivotally attaching said second loop between said side plates, said second retainer means being slidable within said slots whereby said second loop is free to move longitudinally between said two side plates over the length of said slots as the middle portion of said spring flexes outwardly and inwardly relative to said top plate;

means for varying the effective length of said slots thereby varying the amount of flexing of said spring relative to said top plate.

2. A centralizer according to claim 1, wherein said means for varying the effective length of said slots consists of at least one stop element attached to at least one of said side plates, across said slot in said side plate.

3. A centralizer comprising:

an elongated support having a top plate and spaced apart side plates depending one each from the longitudinal edges of said top plate;

two registering perforations provided one each in corresponding first end portions of said end side plates and a first opening in said top plate proximate said perforations;

two registering longitudinally elongated slots provided one each in corresponding second end portions of said side plates and a second opening in said top plate proximate and at least as long as said slots;

an elongated longitudinally curved leaf spring having first and second ends received in said first and second openings in said top plate, said spring being prestressed into an outwardly curved arcuate configuration;

means pivoting one end of said leaf spring with said registering perforations in said support side portions; and

a retainer element afiixed to the other end of said spring slidably received in said elongated slots.

4. A centralizer according to claim 3 including a first substantially closed circular loop integrally provided on said first end of said spring, the axis of said loop extending substantially perpendicular and length of said spring;

a pin received in said first integral loop portion and extended through said registered perforations in said support side plates;

a second substantially closed integral circular loop provided on said second end of said spring, the axis of said second loop portion extending substantially perpendicular the length of said spring, said second loop portion receiving said retainer element slidably received in said slots.

References Cited by the Examiner UNITED JACOB L. NACKENOFF, Primary Examiner.

CHARLES E. OCONNELL, Examiner.

D. H. BROWN, Assistant Examiner. 

3. A CENTRALIZER COMPRISING: AN ELONGATED SUPPORT HAVING A TOP PLATE AND SPACED APART SIDE PLATES DEPENDING ONE EACH FROM THE LONGITUDINAL EDGES OF SAID TOP PLATE; TWO REGISTERING PERFORATIONS PROVIDED ONE EACH IN CORRESPONDING FIRST END PORTIONS OF SAID END SIDE PLATES AND A FIRST OPENING IN SAID TOP PLATE PROXIMATE SAID PERFORATIONS; TWO REGISTERING LONGITUDINALLY ELONGATED SLOTS PROVIDED ONE EACH IN CORRESPONDING SECOND END PORTIONS OF SAID SIDE PLATES AND A SECOND OPENING IN SAID TOP PLATE PROXIMATE AND AT LEAST AS LONG AS SAID SLOTS; AN ELONGATED LONGITUDINALLY CURVED LEAF SPRING HAVING FIRST AND SECOND ENDS RECEIVED IN SAID FIRST AND SECOND OPENINGS IN SAID TOP PLATE, SAID SPRING BEING PRESTRESSED INTO AN OUTWARDLY CURVED ARCUATE CONFIGURATION; 